1. Field of the Invention
The present invention relates to an ink-jet recording head used for an ink-jet recording device. The present invention relates to an ink-jet recording head provided with means for pressurizing an ink chamber using a piezoelectric element as means for energizing ink.
2. Description of the Related Art
For prior art related to the present invention, technique disclosed in U.S. Pat. No. 5,265,315 and Japanese published unexamined patent application No. Hei5-504740 can be given.
In such prior art, after a silicon oxide film is formed on a monocrystalline silicon substrate by thermal oxidation so that the film is 2500 xc3x85 thick, a lower electrode layer made of aluminum, nickel, chromium or platinum and others is formed so that the lower electrode film is 0.2 xcexcm thick, next lead zirconate titanate (PZT) which is a piezoelectric substance is formed by sol-gel transformation so that it is 2 to 10 xcexcm thick, further after an upper electrode film is laminated, and a through hole in the direction of the thickness of the silicon substrate to be an ink chamber is formed from the rear of the silicon substrate by etching.
To realize the enhancement of resolution and the speedup of printing respectively required for a printer currently, the size of an ink chamber is required to be reduced and simultaneously, a large number of ink chambers are required to be arranged in high density. To obtain required characteristics, miniaturizing an ink chamber, a diaphragm and a piezoelectric film are required to be simultaneously thinned.
If the thickness of a diaphragm and a piezoelectric film is a few xcexcm or less, a method of baking a piezoelectric film after a thin film is sequentially laminated on a substrate and forming an ink chamber afterward is effective for their manufacturing method as described above in relation to the prior art.
However, if a diaphragm and a piezoelectric film are formed according to the above process and constitution, a lower electrode film tries to contract remarkably in the heat treatment of a PZT film and large positive residual stress is accumulated.
The tension by residual stress of the lower electrode film is tensile force and is larger than the tension by residual stress of another film. Therefore, the tension of the diaphragm remarkably increases the rigidity of the diaphragm as a drumhead strongly strained.
The effect of such tension of a diaphragm is not particularly a problem in a conventional type ink-jet recording head in which a diaphragm is formed so that it is 10 xcexcm or thicker. The reason is as follows: For the rigidity of a conventional type thick diaphragm, flexural rigidity dominates and is in proportion to the third power of the thickness of the diaphragm. In the meantime, the rigidity by the tension of the diaphragm is in proportion to the first power of the thickness. Therefore, as a diaphragm becomes thick, flexural rigidity rapidly becomes large and the effect of the tension of the diaphragm relatively rapidly becomes small.
There is a problem that as piezoelectric displacement when a PZT film is driven operates upon the tension of a diaphragm, surplus energy is required and the efficiency of displacement for driving voltage is remarkably deteriorated.
Further, there is a problem that the tension of the diaphragm on a substrate warps the substrate, a failure of joining occurs when the substrate is joined to another substrate and a yield is remarkably deteriorated.
There is also a problem that even if joining is normally done, dispersion occurs in the tension of the diaphragm in the substrate, the characteristic of plural ink chambers becomes uneven and the quality of printing is deteriorated.
Conversely, there is a problem that if the tension of the diaphragm is the tension of compression, the diaphragm is loosened or buckled and the jetting of an ink droplet is unstable. Further, there is a problem that peeling is caused in an interface between the lower electrode film and the PZT film.
The present invention is made to solve these problems and the object is to provide a reliable ink-jet recording head provided with high resolution.
To achieve the above object, the present invention is characterized in that in an ink-jet recording head provided with plural ink chambers included inside a substrate and respectively partitioned by side walls, a diaphragm which is formed on the surface of the substrate, which seals one side of the ink chamber and at least the upper surface of which acts as a lower electrode and a piezoelectric active part provided with a piezoelectric film arranged on the diaphragm corresponding to the ink chamber and an upper electrode formed on the piezoelectric film, the above diaphragm is constituted as a laminated film provided with at least two layers of a layer with positive stress and a layer with negative stress, the tension of the diaphragm is substantially zero or negative because of the above stress of the diaphragm, and tension obtained by adding the tension of the above piezoelectric film to the tension of the diaphragm is positive.
The present invention is also characterized in that in an ink-jet recording head provided with plural ink chambers included inside a substrate and respectively partitioned by side walls, a diaphragm which is formed on the surface of the substrate, which seals one side of the ink chamber and on the lower surface of which an upper electrode is provided and a piezoelectric film arranged on the diaphragm corresponding to the ink chamber and held between the lower electrode and the upper electrode, the above diaphragm is constituted as a laminated film provided with at least two layers of a layer with positive stress and a layer with negative stress, the tension of the diaphragm is substantially zero or negative because of the above stress and tension obtained by adding the respective tension of the piezoelectric film and the upper electrode to the tension of the diaphragm is positive.
In a favorable embodiment, the above diaphragm may be also provided with a silicon oxide layer formed by oxidizing the surface of a monocrystalline silicon substrate and a metal layer to be the above lower electrode laminated on the silicon oxide layer and plural ink chambers respectively partitioned by side walls may be also formed inside the above monocrystalline silicon substrate.
It is desirable that the metal layer to be the lower electrode is a platinum layer formed on the silicon oxide layer directly or via an intermediate layer for example and relationship between the silicon oxide layer and the platinum layer is as follows:
(Thickness of lower electrode film)/(Thickness of silicon oxide film)xe2x89xa60.5.
Further, the above diaphragm may be also provided with a thin film part thinner than the thickness of the diaphragm in a part corresponding to the above piezoelectric active part in at least a part of an area along the periphery of the ink chamber around the piezoelectric active part.
The above diaphragm may be also provided with a silicon oxide layer formed by oxidizing the surface of a monocrystalline silicon substrate and a metal layer to be the lower electrode laminated the silicon oxide layer and at least a part in the direction of the thickness of the lower electrode may be also removed in the above thin film part.
The above thin film part is formed on both sides in the direction of the width of the piezoelectric active part for example.
According to the present invention, the tension of the diaphragm is kept the tension of zero or compression by combining positive stress and negative stress, no tensile force of the diaphragm which remarkably deteriorates the quantity of displacement when a PZT film is driven is generated and the warp of the substrate can be also simultaneously reduced. As positive tension (tensile force) is generated inside a laminated film when positive stress by the contraction of the piezoelectric film is further combined, the looseness of the diaphragm and the peeling of the PZT film are inhibited.
According to the above present invention, the characteristic of the displacement of the diaphragm by the driving of a piezoelectric element can be prevented by the tension of members constituting the diaphragm from being deteriorated. Therefore, ability for jetting an ink droplet can be sufficiently enhanced, keeping driving voltage low. The deterioration of the characteristic by joining and the deterioration of a yield by a failure of joining can be reduced by reducing the quantity of the warp of the substrate until it is small enough. Further, as no looseness is also caused on the diaphragm if the tension of the diaphragm is prevented from being tensile force, the jetting of an ink droplet is prevented from being unstable and peeling is prevented from being caused in an interface between the lower electrode film and the PZT film, the performance of the recording head can be enhanced as much as possible, securing uniformity and reliability and an ink-jet recording head in high density provided with high resolution using thin film technique can be supplied.